Conventionally, when coding digitized television signals, peripheral information of pixels to be transmitted is used for coding for the following reason. That is, an image generally has strong auto-correlation in a neighboring area, and it is more efficient to use data of the neighboring area in case of compression.
Microscopically, however, a strong correlation is found in a flat part where no signal change occurs while little correlation can be found in an edge part of an image where the signal abruptly changes.
In such case, conventionally, the strength of correlation is fully utilized for coding in a part where a strong correlation is found, and in an edge part, a corresponding quantity of information is allocated for carrying out coding, or coding is carried out within such a range that a visual masking effect can be obtained.
Meanwhile, in the conventional coding, a corresponding quantity of information is allocated for carrying out coding in an edge part of an image. Therefore, the reduction in the quantity of information is limited, thus deteriorating the coding efficiency.